Method and device for the production of varying elements

ABSTRACT

The invention relates to a method and a device for producing secondary form features on a circumferentially closed hollow profile. The device comprises an internal high pressure forming tool, into the impression of which a hollow profile blank can be inserted, a branch branching off radially from the impression, into which branch the hollow profile blank can be expanded by means of a fluidic internal high pressure, with the secondary form feature being formed. So that secondary form features configured in virtually any desired manner from the point of view of the form profile can be formed on the hollow profile in a simple manner and in a reliable manner in terms of the process, it is proposed that the device, furthermore, comprises a diaphragm and a pressure generator, by means of which pressure can be applied to the diaphragm via a pressure medium in such a way that the diaphragm, during the expansion, bears in a supporting manner against the forming secondary form feature against the expansion direction. The diaphragm gives way elastically with the progress of the forming of the secondary form feature until the final shape is achieved. In this case, the diaphragm is attached to the tool in such a way as to span the branch outside the longitudinal extent of the impression.

[0001] The invention relates to a method of producing secondary form features according to the preamble of patent claim 1 and to a device for carrying out the same according to the preamble of patent claim 3.

[0002] A method of the generic type or a device of the generic type has been disclosed by U.S. Pat. No. 4,840,053. In this case, a hollow profile is inserted into a split internal high pressure forming tool, the top part of which has a pot-shaped branch branching off from the impression. After an internal high pressure has been exerted inside the hollow profile, the latter expands into the branch and abuts against the contour of the branch, as a result of which the secondary form feature corresponding in shape to the branch is formed. To form the secondary form feature in a controlled and reliable manner in terms of the process, a solid body is displaceably arranged in the branch and supports the end face of the forming secondary form feature. This form of the support, in a manner which is conventional practice by now, is realized by steel punches actively actuated from outside. However, this is only possible in the case of branches or secondary form features whose lateral surface lines of the inside or outside run rectilinearly and parallel to one another, so that the punch can be directed unhindered in the branch.

[0003] The object of the invention is to develop a method of the generic type or a device of the generic type to the effect that secondary form features configured in virtually any desired manner from the point of view of the form profile can be formed on the hollow profile in a simple manner and in a reliable manner in terms of the process.

[0004] This object is achieved according to the invention by the features of patent claim 1 with regard to the method and by the features of patent claim 3 with regard to the device.

[0005] On account of the elastic diaphragm which covers the branch and is in each case under a supporting pressure in the position of use, this supporting pressure always being somewhat below the expanding internal high pressure during the expansion of the hollow profile, on the one hand a sufficient supporting force is quickly offered at all times to the -forming secondary form feature in a simple manner due to the flexible adaptation of the diaphragm to the design conditions of the branch form over a large area, by means of which supporting force the hollow profile material can optimally conform to the wall contour of the branch without running the risk of exceeding the yield point, a factor which would lead to bursting of the hollow profile, and on the other hand, due to the elasticity of the diaphragm, the latter gives way in a true-to-shape manner with regard to the wall contour of the branch, and in the process jamming between the end face of the forming secondary form feature and the branch wall is avoided. Secondary form features which may have virtually any desired cross-sectional changes can be produced on hollow profiles in a reliable manner in terms of the process by the solution according to the invention. Thus it is readily possible to form undercuts, and support of the secondary form feature can be realized from the start of forming even in the case of large transition radii from the longitudinal extent of the tool impression toward the branch. The latter is of considerable advantage for the ensuring of process reliability especially when using materials of low ductility, such as light-metal alloys for example. The arrangement of a diaphragm requires very little outlay in terms of apparatus and can also be retrofitted in existing forming tools in a simple manner.

[0006] Expedient configurations of the invention can be gathered from the subclaims; otherwise, the invention is explained in more detail below with reference to an exemplary embodiment shown in the drawings, in which:

[0007]FIG. 1 shows, in a lateral longitudinal section, a section of a device according to the invention in the undeformed state of the hollow profile, with pressure-relieved diaphragm,

[0008]FIG. 2 shows, in a lateral longitudinal section, a section of the device from FIG. 1 in the undeformed state of the hollow profile, with supporting diaphragm,

[0009]FIG. 3 shows, in a lateral longitudinal section, a section of the device from FIG. 1 during the expansion of the hollow profile into a branch of the forming tool of the device, with supporting diaphragm,

[0010]FIG. 4 shows, in a lateral longitudinal section, a section of the device from FIG. 1 in the final state of the hollow profile with secondary form feature and diaphragm located in the initial position.

[0011] A device for producing secondary form features on a circumferentially closed hollow profile is shown in FIG. 1, this device containing an internal high pressure forming tool 1. Inserted into its impression 2 along its longitudinal extent is a hollow profile blank 3. A branch 4 branches off radially from the impression 2 and passes through the tool 1. The branch 4 is rounded with large radii in the region 5 of the transition to the longitudinal extent of the impression 2. The branch wall 6 locally has a bead 7 approximately centrally, so that the wall 6, with the flank 8 of the bead 7 which faces away from the hollow profile blank 3, has an undercut. An elastic diaphragm 10 belonging to the device spans the branch 4 in such a way as to cover it in a high-pressure-tight manner at its end 9 remote from the hollow profile. For this purpose, the diaphragm 10, with its margin 11, is fastened all round in a clamping manner between the rear side 12 of the forming tool 1 and a clamping plate 14 provided with an aperture 13 in the covering region. As a result, the diaphragm 10 can easily be exchanged in the event of a wear state which is no longer tolerable. To ensure the pressure tightness, the diaphragm 10 is sealed off at its margin 11 relative to the rear side 12 of the forming tool 1 by means of an annular seal 15, and the clamping plate 14 lying on the rear side 12 of the forming tool 1 is sealed off at its underside relative to the latter by means of an annular seal 16. Resting on the clamping plate 14 is a supporting plate 17, against which the diaphragm 10 according to FIG. 1 bears in the relaxed pressure-relieved state. Running in the supporting plate 17 of the device is a pressure passage 18, which on the one hand is connected to a pressure generator and on the other hand opens out on that side 19 of the supporting plate 17 which faces the diaphragm 10. The supporting plate 17, likewise for reasons of pressure tightness, is sealed off relative to the clamping plate 14 by means of an annular seal 20.

[0012] By means of the pressure generator, a pressure medium, which on account of the ease of handling may be liquid or gaseous, is now directed into the pressure passage 18, whereupon, during discharge from the latter, pressure is applied to the diaphragm 10 on the rear side. In this way, and as a result of the elasticity while counterpressure is still absent, the diaphragm 10 is extended in such a way that it abuts against the branch wall 6, with accuracy of contour, on the one hand and against the hollow profile blank 3 on the other hand (FIG. 2). In the process, an internal high pressure can already be applied in the hollow profile blank 3. In this phase, this internal high pressure is either not yet so high that it has an expanding effect, or certainly corresponds to an expansion pressure, but in this case the supporting pressure extending the diaphragm 10 is equally high, so that deformation of the hollow profile blank 3 into the branch 4 still cannot take place. As an alternative to said pressure media, mechanical expanding devices are also conceivable in which, for example, an elastically deformable body of solid rubber is deformed by a punch, as a result of which the rubber mass displaced in the process presses the diaphragm 10 against the contour of the branch wall 6.

[0013] Once the diaphragm 10 has been placed against the blank 3, the supporting pressure and the expansion pressure are increased, the ratio of the expansion pressure to the supporting pressure during the expansion phase having to be such that, on the one hand, the expansion pressure is considerably greater than the supporting pressure so that the blank 3 is expanded. On the other hand, the supporting pressure must not be so low relative to the expansion pressure that bursting of the blank 3 occurs. The pressure ratios must in particular be arranged in such a way that a certain stress state is formed within the blank material, this stress state permitting a reliable expansion in terms of the process. As the expansion progresses, the expansion pressure is increased in the process. As a result, according to FIG. 3, the blank 3, at the location of the branch 4, is arched into the latter, the diaphragm 10, which acts in a pressure-loaded manner against the expansion direction, being thrust back by the arch 21.

[0014] The diaphragm 10 is advantageously made of a low-friction material or is provided with a low-friction coating, so that the friction of the arch 21 of the blank 3 on the diaphragm 10 is as low as possible and thus the blank 3 is not stretched out in the region of the supporting contact with the diaphragm 10. This contributes to the process reliability of the expansion.

[0015] With the progress of the forming of the secondary form feature 23 until the final shape is achieved, the diaphragm 10 gives way elastically. At the end of the expansion, the finished hollow profile 22 now has a secondary form feature 23 which bears virtually completely against the entire contour of the branch 4 (FIG. 4). The diaphragm 10 now assumes its initial position and is supported on the rear side by the supporting plate 17 covering the branch 4 at the location of the final position of the end face 24 of the secondary form feature 23. In this case, it may prove to be appropriate if the side 19 of the supporting plate 17 is contoured in accordance with the desired shape of the end face 24 of the secondary form feature 23. The end face 24 abuts in the process with accuracy of contour against the rigid supporting plate side 19. In this last phase, the supporting pressure decreases to atmospheric pressure. The internal high pressure in the hollow profile 22 is then also released and said hollow profile 22 is removed from the tool 1.

[0016] As mentioned above, the diaphragm 10 is attached to the tool 1 outside the longitudinal extent of the impression 2. Instead of the clamping, any other releasable means, such as screwed connections for example, may also be used. Alternatively, it is conceivable for an annular recess to be set inside the branch 4, in which recess the diaphragm 10 is fastened in such a way as to span the branch. In this case, an additional clamping plate 14 may be dispensed with in a component-saving manner.

[0017] The supporting plate 17 can be at a distance from the diaphragm 10 unloaded with regard to a supporting and/or internal high pressure. This advantageously achieves the effect that a pressure space is formed between the diaphragm 10 and the supporting plate 17, by means of which pressure space the diaphragm 10 can very rapidly achieve its supporting function on account of the application of pressure now made possible over a wide area. The supporting function of the supporting plate 17 is also retained to a certain extent, since the diaphragm 10, as viewed from the hollow profile blank 3, can extend outward beyond its initial position and come to bear against the supporting plate 17. The diaphragm 10, in the end region of the secondary form feature 23, will certainly be clamped in place between the latter and the branch wall 6, but the finished hollow profile 22 can readily be removed from the forming tool 1 on account of the low friction between hollow profile 22 and diaphragm 10.

[0018] The final position of the end face 24 of the secondary form feature 23 may also be at a distance from the pressure-relieved position of the diaphragm 10. In this case, it is advantageous that, after completion of the expansion operation and pressure relief, the diaphragm 10 springs back from a clamped state into the initial position. In this case, it is ensured that the diaphragm 10 does not adhere to the end face 24 of the secondary form feature 23 and that there is no jamming between the latter and the branch wall 6. However, this variant is only appropriate in the case of secondary form features 23 in which special contouring of the end face 24 is not involved. Furthermore, the supporting plate 17 may be omitted in a component-saving manner. To this end, the pressure medium may also be fed to the diaphragm 10 in another way. After the end of the expansion, first the internal high pressure and then the supporting pressure are released, so that the desired final position of the end face 24 can be maintained and no further forming takes place. The pressure ratio of supporting pressure and internal high pressure may also be such that, in the final phase of the expansion, the supporting pressure increases until it is virtually equal to the internal high pressure in the final position of the end face 24. The expansion stops as a result. Both pressures must then be reduced simultaneously to the same extent, so that forming does not continue.

[0019] This condition can be brought about by the device comprising a bypass line which connects the pressure line of the internal high pressure to the pressure line of the supporting pressure. Arranged for this purpose in the bypass line is a controllable valve which keeps the bypass line closed during the expansion and opens the bypass line after the final position of the end face 24 of the secondary form feature 23 has been reached. In this case, a pressure balance is created in a relatively simple manner which makes it possible to ensure the form of the secondary form feature 23. The pressure control described can be used in all the device variants within the scope of the invention in the last phase of the expansion and then takes the place of the other pressure controls described. 

1. A method of producing secondary form features on a circumferentially closed hollow profile, a hollow profile blank being expanded by means of a fluidic internal high pressure into a branch branching off from an impression of the internal high pressure forming tool, with the secondary form feature being formed, characterized in that the forming secondary form feature (23), by means of a diaphragm (10) to which an external pressure is applied, is supported against the expansion direction during the expansion in such a way that the diaphragm (10) gives way elastically with the progress of the forming of the secondary form feature (23) until the final shape is achieved.
 2. The method as claimed in claim 1, characterized in that the secondary form feature (23) is supported by a supporting pressure which increases with the progress of the expansion.
 3. A device for producing secondary form features on a circumferentially closed hollow profile, having an internal high pressure forming tool, into the impression of which a hollow profile blank can be inserted, a branch branching off radially from the impression, into which branch the hollow profile blank can be expanded by means of a fluidic internal high pressure, with the secondary form feature being formed, characterized in that the device comprises a diaphragm (10) and a pressure generator, by means of which pressure can be applied to the diaphragm (10) via a pressure medium in such a way that the diaphragm (10), during the expansion, bears in a supporting manner against the forming secondary form feature (23) against the expansion direction, the diaphragm (10) giving way elastically with the progress of the forming of the secondary form feature (23) until the final shape is achieved, and in that the diaphragm (10) is attached to the tool (1) in such a way as to span the branch (4) outside the longitudinal extent of the impression (2).
 4. The device as claimed in claim 3, characterized in that the diaphragm (10) is fastened in an annular recess inside the branch (4).
 5. The device as claimed in claim 3, characterized in that the diaphragm (10) is fastened to the rear side (12) of the impression-carrying forming tool (1) at the end (9) of the branch (4).
 6. The device as claimed in one of claims 3 to 5, characterized in that the device contains a supporting plate (17) which covers the branch (4) at the location of the final position of the end face (24) of the secondary form feature (23) on the rear side of the diaphragm (10).
 7. The device as claimed in claim 6, characterized in that the supporting plate (17) is at a distance from the diaphragm (10) unloaded with regard to a supporting and/or internal high pressure.
 8. The device as claimed in either of claims 6 or 7, characterized in that a pressure passage (18) runs in the supporting plate (17), this pressure passage (18) being connected to the pressure generator on the one hand and opening out on sides of the diaphragm (10) on the other hand.
 9. The device as claimed in one of claims 3 to 8, characterized in that the final position of the end face (24) of the secondary form feature (23) is at a distance from the pressure-relieved position of the diaphragm (10).
 10. The device as claimed in one of claims 3 to 9, characterized in that the pressure medium transmitting the supporting pressure is liquid or gaseous.
 11. The device as claimed-in one of claims 3 to 10, characterized in that the diaphragm (10) is made of a low-friction material or is provided with a low-friction coating.
 12. The device as claimed in one of claims 3 to 11, characterized in that the device comprises a bypass line which connects the pressure line of the internal high pressure to the pressure line of the supporting pressure and contains a controllable valve which keeps the bypass line closed during the expansion and opens the bypass line after the final position of the end face (24) of the secondary form feature (23) has been reached. 